1. Field of the invention
The present invention relates to a chip coil and a manufacturing method thereof. More specifically, the present invention relates to a chip coil which includes a coil conductor formed on an insulating substrate and a pair of terminal electrodes formed on both ends of the insulating substrate and connected to both ends of the coil conductor, and a manufacturing method thereof.
2. Description of the prior art
In a conventional chip coil 1 shown in FIG. 5, by means of screen printing Ag paste, a spiral coil conductor 3 is formed on a surface of an alumina substrate 2 and terminal electrodes 4a and 4b are formed on both ends of the alumina substrate 2. The outermost end of the coil conductor 3 is connected to one terminal electrode 4a and the innermost end of the coil conductor 3 is connected to the terminal electrode 4b by a connecting electrode 6 which is formed on a rear surface of the alumina substrate 2 through a throughhole 5 formed in the alumina substrate 2.
In such a conventional chip coil 1, the coil conductor 3 and the terminal electrodes 4a and 4b are formed by means of a screen printing method. Therefore, it was impossible to make a line width of the coil conductor 3 less than 150 .mu.m. In addition, it was impossible to make a diameter of the throughhole 5 formed in the alumina substrate 2 less than 200 .mu.m since if and when the diameter of the throughhole 5 is less than 200 .mu.m, it is difficult to form a metallized layer for the connecting electrode 6 in the throughhole 5. Therefore, in the conventional manufacturing method, it was impossible to obtain a chip coil which is miniaturized and has good reliability.
A method capable of solving such a problem is disclosed in the Japanese Patent Application Laid-open No. 110009/1980 laid-open on Aug. 25, 1980. In the prior art disclosed in the Japanese Patent Application Laid-Open No. 110009/1980, a conductive film is formed on the whole main surface of an insulating substrate by means of vacuum evaporation, and by etching the conductive film, a plurality of strip conductors are formed on the main surface at a predetermined interval. By painting or applying an insulation film made of polyimide on portions of the strip conductors except for respective both ends thereof and forming further strip conductors on the insulation film, a coil conductor in which the ends of the respective strip conductors are connected to each other can be formed.
By the method disclosed in the Japanese Patent Application Laid-open No. 110009/1980, since the plurality of strip conductors are formed by etching, it is possible to make a line width of the coil conductor smaller than that of the conventional method, and it is not necessary to form a throughhole for connecting the terminal electrodes to the coil conductor or to employ a wire-bonding technique. Therefore, there was an advantage that a chip coil which is miniaturized can be obtained.
However, in the method disclosed in the Japanese Patent Application Laid-open No. 110009/1980, it is necessary to paint or apply the insulation film on only middle portions of the respective strip conductors such that the both ends of the respective strip conductors can be exposed. However, a work for painting or applying the insulation film such that only the both ends of the fine strip conductors can be accurately exposed is very difficult, and therefore, dimensional precision becomes low due to such difficulty. Therefore, a problem occurs in reliability of the chip coil.